1. Field of the Invention
The present invention relates to an inkjet recording head which is provided during distribution with a protective tape on a discharge port forming surface, which is a surface on which discharge ports are formed. More specifically, the present invention relates to an inkjet recording head which can be suitably protected by a protective tape and from which the protective tape can be suitably peeled off as a result of suitably configuring the structure of the discharge port forming surface on which the protective tape is provided.
2. Description of the Related Art
Generally, inkjet recording heads which are mounted on an inkjet recording apparatus are provided with a protective member on the discharge port forming surface to ensure safe distribution. As one configuration example, a configuration such as that illustrated in FIG. 12, which is discussed in Japanese Patent Application Laid-Open No. 03-176156 (U.S. Pat. No. 5,850,238), is known. In this example, a configuration is employed which ensures the reliability of the sealing properties by covering a discharge port forming surface H2 of an inkjet recording head H1 with a protective tape C2, and further covering the protective tape C2 with a cap member C1. As a result of this configuration, evaporation of moisture from the discharge ports is suppressed, so that clogging of the discharge ports due to increased viscosity of the ink can be prevented, or adhesion of surrounding dust and the like to the discharge port periphery and to the discharge ports can be prevented.
A configuration is employed in which an adhesive layer is provided on the protective tape for protecting the discharge ports, and the protective tape is adhered to the discharge port forming surface. In a protective tape having such an adhesive layer, if a suitable adhesive layer is not formed, the adhesive material forming the adhesive layer may intrude into the discharge ports, or remain on the discharge port forming surface when the protective tape is peeled off, thereby affecting discharge. To resolve this problem, for example, the configuration illustrated in FIGS. 13A and 13B, which is discussed in Japanese Patent Application Laid-Open No. 2000-313117 (U.S. Pat. No. 6,578,956), has been proposed. This configuration is directed to making it easier for the protective tape to be peeled off and harder for the adhesive material to remain on the discharge port forming surface, by employing a configuration in which the adhesion surface area per unit area of the protective tape C2 in the periphery H20 of the discharge port forming surface H2 is decreased.
In inkjet recording, to achieve high-quality color recording equal to silver halide photography, a head configuration has been employed in which the size of the ink droplets discharged from the inkjet recording head is decreased to small dots so that the dots cannot be easily seen (a grainy effect is not noticeable) on the recorded object. For example, as the small dot ink droplets, the size of the dots has had to be around 5 pL (picoliters, 10-12 liters), with a dot size of 40 to 50 μm and a resolution of 600×1200 to 1200×1200 dpi (dpi is a unit representing the number of dots per inch).
However, to respond to the needs of users who wish to further mitigate grainy effects in the halftone and highlight portions in recent color photo images, it has become required to discharge even smaller dot ink droplets at an even higher density.
For an inkjet recording head which discharges ink by utilizing heat, an often-used configuration has a nozzle member in which a predetermined number of electrothermal transducers are formed on an upper layer of a substrate, and ink channels corresponding to the electrothermal transducers and discharge ports in communication with the respective ink channels are formed on the substrate. Since it is easy to change the dimensions of the discharge ports and ink channels, which affect the discharge amount of ink droplets, such a head configuration is suitable for an inkjet recording head for high-definition recording which discharges minute ink droplets.
As illustrated in FIG. 14, especially the peripheral portion of the discharge ports 6 of the recording head having such a nozzle member is a hollow structure, because it has an ink channel 7 and an electrothermal transducer 2 in its interior. As a result, the discharge port forming surface tends to be fragile against an external force. When discharging smaller dot ink droplets at a higher density, the pitch between each of the ink channels inevitably becomes narrower, so that the proportion of the nozzle member taken up by the ink channels, in other words, the proportion of the hollow structure, increases. Therefore, the strength of the discharge port forming surface against an external force decreases even further. If a conventional discharge port protective tape is employed on an inkjet recording head having such a structure, the adhesive force of the adhesive layer is too high, so that when the protective tape is peeled off cracks may be caused on the discharge port peripheral portions due to that peeling force. In extreme cases, the member forming discharge ports (nozzle member) may even be peeled off from the substrate.
To prevent such a phenomenon, for example, it has been proposed to reduce the peeling force of the tape by changing the type of adhesive material of the protective tape, and for example as discussed in Japanese Patent Application Laid-Open No. 2006-212796, by adjusting the adhesion region on the protective tape side. According to these measures, the above-described problems of cracking and peeling on the discharge port peripheral portions can be avoided. However, because the adhesive strength between the discharge port forming surface and the protective tape is decreased, the phenomenon of ink seeping from the discharge ports can arise. Especially for a recording head having discharge ports which discharge a plurality of colors in a single head, for example, cyan, magenta, and yellow, ink seepage can cause a phenomenon in which ink that has seeped from a discharge port mixes with other colors, and this mixed color ink is sucked back into the original discharge port to cause color mixing as far as inside the ink channel.
Further, for an inkjet recording head having a configuration which can discharge ink droplets in a plurality of sizes, for example, about 5 pL and 2 pL, discharge ports and ink channels having different dimensions according to the discharge amount of the ink droplets are intermingled. At each differently-shaped discharge port peripheral portion, the strength against an external force is different. To prevent color mixing due to cracks caused on the discharge port peripheral portions and ink seepage from a discharge port, the proposals which have been made up until now for properly setting the peeling force of the protective tape are not sufficient. For example, even if the protective tape adhesive material and the type of protective tape itself are changed, the selection of that material is difficult. Further, even if the adhesion region on the protective tape side is adjusted, adjusting the positional relationship between the adhesion region and the discharge ports is very complex.
Regarding adjusting the adhesion properties between the protective tape and the discharge port forming surface, as illustrated in Japanese Patent Application Laid-Open No. 2000-313117 (U.S. Pat. No. 6,578,956), a configuration which decreases the adhesive force by reducing the adhesion surface area of the regions away from the discharge ports of the inkjet recording head may also be considered. For example, several techniques for adjusting the structure of the surface of the discharge port forming surface have been proposed. One example is Japanese Patent Application Laid-Open No. 2006-175657 (U.S. Patent Application Publication No. US 2006/0115598) illustrated in FIGS. 15A and 15B. However, in this proposal, the concept is only from the perspective of improving the discharge state of the ink. There is no discussion of a concept from the perspective of adjusting the adhesion properties between the protective tape and the discharge port forming surface during distribution.